1. Technical Field
The present invention relates to a display medium using mobile fine particles that is utilizable as an optical device, such as a light-modulating glass, a light-modulating device, a display device, or the like, and a display device and a display method using the display medium.
2. Related Art
With the progress of the highly information-oriented society, there has been an increased need for electronic paper systems, color display systems, and large-area display systems. In order to meet such needs, display technologies, such as CRT, liquid crystal, EL, LED, plasma, and the like, have been developed. In addition to these self-light emitting systems, development of a reflection-type display system which consumes less power and gives a less sense of incongruity to the human eye has been investigated. Promising reflection-type display systems include those utilizing reflection-type liquid crystal technologies, and the like.
On the other hand, while there is a great need for next-generation electronic paper display systems, no promising technology for meeting the need has yet been established at present. Known candidate methods include an electrophoretic method, a liquid crystal method, an organic EL method, and the like.
Since the liquid crystal method is a filter method, it is difficult to decrease the thickness and weight of the medium, and the organic EL method has presented a problem in that, due to the self-light emitting nature, it has no memorizability, resulting in the scope of application being limited.
On the other hand, for the display device using the electrophoretic method, the following technologies have been disclosed.
For example, a method which disposes microcapsules encapsulating a dispersant and electrophoretic particles between a pair of electrodes has been disclosed (as in Japanese Paten Laid-Open Publication (JP-A) No. 64-86116, for example). In addition, the magnetic electrophoretic method which uses microcapsules containing a magnetic fluid has been reported (as in JP-A No. 4-199085/1992, for example).
Further, a method which disposes a plurality of colored particles in a single microcapsule in a mixed state, and selectively drives these particles has been disclosed (as in U.S. Pat. No. 6,017,584, for example).
However, microcapsules are used any of these methods, making it difficult to have a fine dot display or a full-color display. In JP-A No. 64-86116, the number of colors which can be displayed concurrently is two, which has rendered multicolor display (color display) difficult. In U.S. Pat. No. 6,017,584, it has been fundamentally difficult to drive the particles selectively.
In addition, a configuration in which charged electrophoretic particles are disposed in approximately equal amounts in a plurality of divisions provided along the surface of a pair of substrates disposed with a predetermined spacing being given, the dispersant being blue, and the charged electrophoretic particles being black, has been stated with a report that the display quality can be improved (as in JP-A No. 2000-322004, for example).
However, with this configuration, full colorization is difficult, and the lamination would make it impossible to realize color reproduction using the subtractive mixture method by the combination with the particles in the respective layers. Thus it is inevitable to take parallel disposition, which has presented a problem in that the apparatus becomes intricate.
Further, a method which disposes cells or microcapsules for expressing a plurality of colors to carry out color display has been disclosed (as in JP-A No. 2000-35598, for example. However, there is a problem in that sufficient contrast cannot be obtained.
Additionally, a method which vertically laminates two or more electrophoretic sections including particles/mediums having light permeability has been disclosed (as in JP-A No. 2002-333643, for example). However, dyestuffs are used in order to color the particles, and thus sufficient light-modulating density cannot be obtained.
On the other hand, a method which provides a plurality of accommodation sections for accommodating fine particles which have been electrophoresed has been disclosed (as in JP-A No. 2002-162649, for example). However, to carry out color display, particles different in color must be disposed in parallel, and thus there is no color reproducibility, and high contrast cannot be obtained.
In addition, a method which lamination-disposes or parallel-disposes cells comprising two display electrodes disposed in superposed positions, two collect electrodes, and two types of light permeable colored particle has been disclosed (as in JP-A No. 2004-20818, for example). However, since relatively large particles colored with dyestuffs are used, sufficient light-modulating density cannot be obtained, and stability of the light-modulating agent has been a problem.
As can be seen from the above description, with the electrophoretic method, many problems need to be solved in order to obtain a color display excellent in coloration, and technology for solution thereof has been demanded.